Editing IPCC:AR6/WGI/Chapter-4 (section)

==== 4.6.1.2 Precipitation ====

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While global mean precipitation increases as GSAT rises with the ''very likely'' range of 1–3% per 1°C ( ''high confidence'' ) (Sections 8.2.1 and 8.4.1), patterns of precipitation change do not scale as linearly with GSAT increase. Nevertheless, common features of precipitation change in the multi-model mean across scenarios still exist for different levels of global warming (Figure 4.32). Precipitation will ''very likely'' increase in the high latitudes and over tropical regions, and will ''likely'' increase in large parts of the monsoon region, but are ''likely'' to decrease over the subtropical regions, including the Mediterranean, southern Africa, parts of Australia and South America at all four levels of global warming. The increases and decreases in precipitation will amplify at higher levels of global warming ( ''high confidence'' ) (Figure 4.32). Changes in extreme precipitation events under different levels of global warming are assessed in Chapter 11.

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[[File:03b9f70ce7cce3b59a103943cd279d67 IPCC_AR6_WGI_Figure_4_32.png]]

'''Figure 4.32 |''' '''Projected spatial patterns of change in annual average precipitation (expressed as a percentage change) at different levels of global warming.''' Displayed are '''(a–d)''' spatialpatterns of change in annual precipitation at 1.5°C, 2°C, 3°C, and 4°C of global warming relative to the period 1850–1900. No map overlay indicates regions where the change is robust and ''likely'' emerges from internal variability, that is, where at least 66% of the models show a change greater than the internal-variability threshold ( [[#4.2.6|Section 4.2.6]] ) and at least 80% of the models agree on the sign of change. Diagonal lines indicate regions with no change or no robust significant change, where fewer than 66% of the models show change greater than the internal-variability threshold. Crossed lines indicate areas of conflicting signals where at least 66% of the models show change greater than the internal-variability threshold but fewer than 80% of all models agree on the sign of change. Values were assessed from a 20-year period at a given warming level, based on model simulations under the Tier-1 SSPs of CMIP6. Further details on data sources and processing are available in the chapter data table (Table 4.SM.1).

The SR1.5 stated ''low confidence'' regarding changes in global monsoons at 1.5°C versus 2°C of global warming, as well as differences in monsoon responses at 1.5°C versus 2°C. Generally, statistically significant changes in regional annual average precipitation are expected at a global mean warming of 2.5°C–3°C or more ( [[#Tebaldi--2015|Tebaldi et al., 2015]] ). Over the austral-winter rainfall regions of south-western South America, South Africa and Australia, projected decreases in mean annual rainfall show '''high agreement''' across models and a strong climate change signal even under 1.5°C of global warming, with further amplification of the signal at higher levels of global warming ( ''high confidence'' ) ( [[#Mindlin--2020|Mindlin et al., 2020]] ). This is a signal evident in observed rainfall trends over these regions (Sections 2.3.1.3 and 8.3.1.6 ). Also, over the Asian monsoon regions, increases in rainfall will occur at 1.5°C and 2°C of global warming ( [[#Chevuturi--2018|Chevuturi et al., 2018]] ). At warming levels of 1.5°C and 2°C, the changes in global monsoons are strongly dependent on the modelling strategies used, such as fully coupled transient, fully coupled quasi-equilibrium, and atmosphere-only quasi-equilibrium simulations. In particular, the differences of regional monsoon changes among model setups are dominated by strategy choices such as transient versus quasi-equilibrium set-up, prescription of SST, and treatment of aerosols ( [[#Zhang--2021|Zhang and Zhou, 2021]] ).

The global and land area fractions with significant precipitation changes with global warming are shown in Figure 4.33. It is ''virtually certain'' that average warming will be higher over land. As warming increases, a larger global and land area will experience statistically significant increases or decreases in precipitation ( ''medium confidence'' ). The increase of the area fraction with significant precipitation increase is larger over land than over the ocean, but the increase of the area fraction with significant precipitation decrease is larger over the ocean than over land (Figure 4.33). Precipitation variability in most climate models increases over the global land area in response to warming ( [[#Pendergrass--2017|Pendergrass et al., 2017]] ).

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[[File:234ba024605e8d9502eda050a0989ea3 IPCC_AR6_WGI_Figure_4_33.png]]

'''Figure 4.33''' '''|''' '''Area fraction of significant precipitation change at 1.5°C, 2°C, 3°C, and 4°C of global warming.''' Range of land fraction '''(top)''' and global area fraction '''(bottom)''' with significant precipitation increase '''(left-hand side)''' and decrease '''(right-hand side)''' in the projected annual precipitation change (%) at levels of global warming compared to the period 1850–1900. Values were assessed from a 20-year period at a given warming level from SSP1-2.6, SSP3-7.0 and SSP5-8.5 in CMIP6. The solid line illustrates the CMIP6-multi model mean and the shaded band is the 5–95% range across models that reach a given level of warming. Further details on data sources and processing are available in the chapter data table (Table 4.SM.1).

In summary, based on the assessment of CMIP6 models, there is ''high confidence'' that global mean precipitation will increase with increase in global mean surface temperature. Precipitation will ''very likely'' increase in the high latitudes and over tropical regions, ''likely'' increase in large parts of the monsoon region, but will ''likely'' decrease over the subtropical regions. There is ''high confidence'' that increases and decreases in precipitation will amplify over higher levels of global warming. As warming increases, there is ''medium confidence'' that a larger land area will experience statistically significant increases or decreases in precipitation.

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